This paper describes an investigation of the role of nickel phthalocyanine-tetrasulfonic acid (NiPcTs) for methanol electro-oxidation on a Pt/C catalyst. Cyclic voltammetry (CV) revealed that NiPcTs has no catalytic activity in methanol or CO electro-oxidation. However, methanol electro-oxidation occurs faster on a Pt/C catalyst modified with NiPcTs than on the original Pt/C catalyst. CO stripping results demonstrated that NiPcTs promotes electro-oxidation of adsorbed CO (COads) on the Pt/C catalyst, which is likely to be responsible for the enhancement of the methanol electro-oxidation rate. The promotion effect of NiPcTs is attributable to its ability to modify the electron density of the Pt surface. The electron deficiency of Pt-0 in the NiPcTs-Pt/C catalyst is shown by the shift of the Pt-0 4f peak to higher binding energies in the X-ray photoelectron spectrum.